1. Technical Field
The present invention relates to a piezoelectric device and a method for manufacturing a piezoelectric device.
2. Related Art
In piezoelectric devices as typified by a piezoelectric resonator and a piezoelectric oscillator, for example, that are used in various electronic devices such as information equipment and mobile communication equipment, the following structure is known as a sealing structure of a package.
JP-A-2002-9577, for example, discloses the structure. In the structure, a portion (a base portion) of a package has a stepped opening composed of a first hole and a second hole. The first hole has a predetermined diameter and is opened inward the package, while the second hole has a larger diameter than the first hole and is opened outward. A metal coat is provided to a stepped part that is a bottom part of the second hole and to an inner periphery surface of the second hole. Further, a sealant is put in the opening and melted so as to seal the opening.
In the piezoelectric device of the above example, the base portion is composed of two ceramic substrates. The first hole and the second hole are respectively formed on these ceramic substrates, and the ceramic substrates are layered so as to form the stepped opening (hereinafter, referred to as a through hole). Therefore, the ceramic substrates may be layered in a manner to position the first hole and the second hole eccentric to each other. As a result, in the piezoelectric device, a distance from the inner periphery surface of the first hole to the inner wall surface of the second hole in the through hole is not even throughout the whole circumference. Therefore, the sealant that is melted does not evenly spread, forming a void (a bubble) disadvantageously.
Further, in the piezoelectric device described above, the sealant having a spherical shape is melted by being irradiated with a laser beam or the like so as to seal the through hole. At this time, the sealant does not spread inside the first holes but spreads to cover the first hole. The thickness of the sealant after the sealing is small at the center part of the second hole and large at the inner wall surface part due to wettability. An amount of the sealant is set depending on a volume of the through hole. If the amount is too large, the sealant flows out of the through hole to the external side of the package in the sealing. A through hole is commonly formed at a mounting side on external equipment, so that the overflow of the sealant may adversely affect the mounting of the device on the external equipment.
Therefore, in the piezoelectric device, more amount of sealant can not be put in the through hole, so that the smaller amount of the sealant caused by variation may produce an opening in a part having smaller thickness in the melting of the sealant.
Thus, the piezoelectric device has a problem of a sealing defect of the package and a problem that a piezoelectric resonator element stored in the package is irradiated with a laser beam or the like that passes through the opening and is damaged.
In order to prevent the damage of the piezoelectric resonator element caused by the opening in the sealant, the metal coat is provided to the inner wall surface of the first hole so as to allow the sealant to spread in the inner wall surface of the first hole as well and thus fill the first hole with the sealant (refer to FIG. 9 of JP-A-2002-9577, for example). However, in this case, the sealant that fills the first hole may overflow from the first hole to the inside of the package and contact with the piezoelectric resonator element, reducing the vibrating performance of the piezoelectric resonator element.
In order to prevent the overflow of the sealant to the inside of the package, a forming range of the metal coat is set to be up to the halfway position of the inner wall surface of the first hole.
However, in this case, a technique to form the metal coat up to the halfway position is not established, so that it is hard to manufacture components at a mass-production level.